An easy option is to use your own Mac "Console" application
Logs from iPhone
Connect your phone to the computer via USB.
From 'Devices' section, choose your phone and see the logs appear.
Before reproducing your issue "clear display" and after reproducing make sure to copy-paste the log into .txt file.
NB! When you are ready to save the file, always do so in .txt format.
Another option is to use xCode, check out the tutorial below
Window - > Devices - > Select your device from left side list
On the bottom, after the Installed Apps list, you have a little Arrow to expand logs.
After you reproduce the issue tap on the download arrow from the bottom right part of the Devices window.