diff --git a/Example/Auth/Tests/FIRPhoneAuthProviderTests.m b/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
index 564f888fcb3..18b5db918bb 100644
--- a/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
+++ b/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
@@ -43,7 +43,6 @@
 #import "FIRVerifyClientResponse.h"
 #import "OCMStubRecorder+FIRAuthUnitTests.h"
 #import "Phone/FIRPhoneAuthCredential_Internal.h"
-#import "Phone/NSString+FIRAuth.h"
 
 @import SafariServices;
 
@@ -328,7 +327,6 @@ - (void)testVerifyPhoneNumber {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -443,7 +441,6 @@ - (void)testVerifyPhoneNumberUIDelegate {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -711,7 +708,6 @@ - (void)testVerifyClient {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -893,7 +889,6 @@ - (void)testSendVerificationCodeSuccessFulRetry {
                     completion:^(NSString *_Nullable verificationID, NSError *_Nullable error) {
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
diff --git a/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m b/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
index 3a098a56827..fd4ce58279f 100644
--- a/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
+++ b/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
@@ -20,7 +20,6 @@
 
 #import "FIRLogger.h"
 #import "FIRPhoneAuthCredential_Internal.h"
-#import "NSString+FIRAuth.h"
 #import "FIRApp.h"
 #import "FIRAuthAPNSToken.h"
 #import "FIRAuthAPNSTokenManager.h"
@@ -194,8 +193,6 @@ - (void)verifyPhoneNumber:(NSString *)phoneNumber
               callBackOnMainThread(nil, error);
               return;
             }
-            // Associate the phone number with the verification ID.
-            response.verificationID.fir_authPhoneNumber = phoneNumber;
             callBackOnMainThread(response.verificationID, nil);
           }];
         }];
@@ -381,8 +378,6 @@ - (void)verifyClientAndSendVerificationCodeToPhoneNumber:(NSString *)phoneNumber
         callback(nil, error);
         return;
       }
-      // Associate the phone number with the verification ID.
-      response.verificationID.fir_authPhoneNumber = phoneNumber;
       callback(response.verificationID, nil);
     }];
   }];
diff --git a/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.h b/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.h
deleted file mode 100644
index ba123faabe2..00000000000
--- a/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.h
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright 2017 Google
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#import <Foundation/Foundation.h>
-
-NS_ASSUME_NONNULL_BEGIN
-
-/** @category NSString(FIRAuth)
-    @brief A FIRAuth category for extending the functionality of NSString for specific Firebase Auth
-        use cases.
- */
-@interface NSString (FIRAuth)
-
-/** @property fir_authPhoneNumber
-    @brief A phone number associated with the verification ID (NSString instance).
-    @remarks Allows an instance on NSString to be associated with a phone number in order to link
-        phone number with the verificationID returned from verifyPhoneNumber:completion:
- */
-@property(nonatomic, strong) NSString *fir_authPhoneNumber;
-
-@end
-
-NS_ASSUME_NONNULL_END
diff --git a/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.m b/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.m
deleted file mode 100644
index 87f3b1c9430..00000000000
--- a/Firebase/Auth/Source/AuthProviders/Phone/NSString+FIRAuth.m
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright 2017 Google
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#import "NSString+FIRAuth.h"
-
-#import <objc/runtime.h>
-
-NS_ASSUME_NONNULL_BEGIN
-
-@implementation NSString (FIRAuth)
-
-- (void)setFir_authPhoneNumber:(NSString *)phoneNumber {
-  objc_setAssociatedObject(self, @selector(fir_authPhoneNumber), phoneNumber,
-                           OBJC_ASSOCIATION_RETAIN_NONATOMIC);
-}
-
-- (NSString *)fir_authPhoneNumber {
-  return objc_getAssociatedObject(self, @selector(fir_authPhoneNumber));
-}
-
-@end
-
-NS_ASSUME_NONNULL_END