I value the efforts you’ve put into addressing this matter, Sarah, and I can assure you that you’re headed in the right direction.
When searching for a mobile number, ensure that you only enter the digits, omitting any characters such as dashes or parentheses. Wait for the pop-up to appear; do not press Enter or click the magnifying glass icon.
For more information on managing your custom fields, please refer to the full article: Manage custom fields in QuickBooks Online.
Additionally, you can check these articles for more help on customizing your forms:
This thread is always open for any additional questions or updates. If you need further assistance with the QuickBooks customer list, feel free to tag me anytime. I'm here to help!