There are 2 settings that effect text size on windows 10 mobile
- Settings > system > display > “set size of text, apps and item on this display”
- Settings > ease of access > More options > “text scaling”
The setting in display works much better to change the text size without getting in the way of everything working nicely.
The setting in ease of access has a much bigger effect on text display, layout etc. Its more likely to have unexpected effects.
And then there’s the “settings sync surprise”.
If you use one account on multiple devices, be very careful about syncing all the settings, such as theme and other things. Better to have sync turned on but don’t sync any of the appearance related settings. Because the device on which the setting is turned on, will push those settings to other devices. And for me that has resulted in messing up my user experience on the other device. I synced settings from my laptop onto my mobile, and then my mobile text became too small to read. The way I undid this problem was to reset my mobile after disabling all the sub-sync settings on my laptop.
I recommend using a different account for each device login account, and having a separate account as the data sync account.
… then login with my data sync account for calendar, onenote, etc. … so that each device has its own unique appearance settings and syncing them all to the cloud, wont mess up another account on a different device.