Text replacement not working on iPhone
The steps to fix this are the same as many data corruption issues.


Back up the phone


Take care to unsync any Apple Watches
Take care to backup health data by choosing an encrypted backup option
Verify a good backup (or two)

Settings app - erase all content and settings
Set up phone as new - test one substitution to ensure it's not needing a full OS restore
Erase content and settings a second time, then restore from backup