Why is my phone restarting after display replacement.

The bracket is there to secure the cables and make them stay in place. If the flex cables aren’t properly secured into place and the bracket is missing, you may want to get a new one. However the phone shouldn’t restart, the display should just be extremely glitchy…

If this only was a display replacement something like this shouldn’t happen. However, the person that did this poor repair might have damaged the logic board at some point. If that would be the case, the phone is more likely to behave weirdly.

You can always try to restore the device back to factory settings and see if that makes a difference, but doing so will wipe your data, so be careful and back up everything you want to keep.

If you’re unlucky the logic board might have been damaged and replacing that would be pretty difficult and expensive…