I have a new 15 Pro and the same issues with USB-C cables. The non-propietary cable I use with my computer works fine with my iPad. It does not work with my phone. We have USB-C cables all over the house because my husband is Android and my new kindle is also USB-C. The cable that came with my computer (too short to be useful with the MacBook Pro) works great with the phone. I have a very short cable that I use with my power bank that works with my phone. Weird. There's a cable in my husband's stash that also works. Many don't, so we took a closer look.
It also seems that my Apple case may be a factor. Some cables have a larger grip for the plug that the opening in the case and won't go in. Slimmer grips/handles give me that satisfying click on my phone. You can see it in the picture. There's quite a difference in the size of the grip for the plug. If you have a case on the phone, it could be blocking the plug. FWIW, the case on my iPad doesn't seem to do that.