After extensive testing, I discovered that to avoid the ‘Phone’ field opening a blank page when attempting to edit its settings, you simply need to preview the form at least once beforehand. Once the form has been previewed, the ‘Phone’ field can be added and its ‘Edit’ option accessed without any issue.
I found the conflict plugin. It is “Chauffeur Booking System for WordPress“. So, now what? how I can solve the issue?
Thanks Amin. I’ll do further tests as suggested.