You can enlarge the texts on smartphone app in the following way.
<iPhone>
1. Open “Settings” app.
2. Tap “Accessibility”.
3. Tap “Display & Text Size”.
4. Tap “Larger Text”.
5. Move the slider on the lower and change the size of texts.
<Android>
1. Open “Settings” app.
2. Tap “Accessibility”.
3. Tap “Font Size”.
4. Move the slider on the lower and change the size of texts.