What to fix when my phone says searching

My phone got dropped from about five feet onto tile floors. A day or so later the “searching” signal appeared. I tried everything i could find online. All the software resets and restarts. The SIM card. Etc. i did try dropping my phone as was suggested and then restarted it. It worked for about a day or so and then went back to searching. Now the “drop method” no longer works. I repair iPhones regularly and thought i would give replacing the part a try. However, i cannot seem to find a certain answer as to what part may be causing the problem if it is a mechanical failure. I have no problem connecting to WiFi, just to the cellular network. What part needs to be replaced, or are there other ways to fix the problem that you would suggest? Thanks in advance!