Update phone verification error message (#1350)

# What this PR does

## Which issue(s) this PR fixes

## Checklist

- [ ] Tests updated
- [ ] Documentation added
- [ ] `CHANGELOG.md` updated

---------

Co-authored-by: Vadim Stepanov <vadimkerr@gmail.com>

grafana-plugin/src/containers/UserSettings/parts/tabs/PhoneVerification/PhoneVerification.tsx

@@ -116,7 +116,7 @@ const PhoneVerification = observer((props: PhoneVerificationProps) => {
         })
         .catch(() => {
           openErrorNotification(
-            "Can't send SMS code. Please try other phone number formats. Don't forget the country code!"
+            'Grafana OnCall is unable to verify your phone number due to incorrect number or verification service being unavailable.'
           );
         });
     }