Open your phone’s Settings app
Tap Display or Display & Brightness
Tap Font size or Text size
Move the slider to adjust the size
Open Messages to check the new size
On iPhone, you can also go to Settings > Accessibility > Display & Text Size > Larger Text
On Android, you may also find font settings under Accessibility or Screen settings
If the text in Messages still looks small, check the app’s zoom or display settings
Restart the Messages app if the change does not appear right away