diff --git a/packages/firebase_analytics/firebase_analytics/ios/firebase_analytics/Sources/firebase_analytics/FirebaseAnalyticsPlugin.swift b/packages/firebase_analytics/firebase_analytics/ios/firebase_analytics/Sources/firebase_analytics/FirebaseAnalyticsPlugin.swift
index fcd6bda21819..80c7b5c43668 100644
--- a/packages/firebase_analytics/firebase_analytics/ios/firebase_analytics/Sources/firebase_analytics/FirebaseAnalyticsPlugin.swift
+++ b/packages/firebase_analytics/firebase_analytics/ios/firebase_analytics/Sources/firebase_analytics/FirebaseAnalyticsPlugin.swift
@@ -136,12 +136,31 @@ public class FirebaseAnalyticsPlugin: NSObject, FLTFirebasePluginProtocol, Flutt
       Analytics.initiateOnDeviceConversionMeasurement(hashedEmailAddress: data)
     }
     if let hashedPhoneNumber = arguments["hashedPhoneNumber"] as? String,
-       let data = hashedPhoneNumber.data(using: .utf8) {
+       let data = hexStringToData(hashedPhoneNumber) {
       Analytics.initiateOnDeviceConversionMeasurement(hashedPhoneNumber: data)
     }
     completion(.success(()))
   }
 
+  private func hexStringToData(_ hexString: String) -> Data? {
+    let length = hexString.count
+    guard length % 2 == 0 else { return nil }
+
+    var data = Data(capacity: length / 2)
+    var index = hexString.startIndex
+
+    for _ in 0 ..< (length / 2) {
+      let nextIndex = hexString.index(index, offsetBy: 2)
+      guard let byte = UInt8(hexString[index ..< nextIndex], radix: 16) else {
+        return nil
+      }
+      data.append(byte)
+      index = nextIndex
+    }
+
+    return data
+  }
+
   public func didReinitializeFirebaseCore(_ completion: @escaping () -> Void) {
     completion()
   }