Make supported text larger
Open Settings, then Accessibility, then Display & Text Size. Choose Larger Text and move the slider. Enable Larger Accessibility Sizes if you need the additional range. Bold Text is a separate choice in the same settings area.
Apple also documents a Text Size control in Control Center. Use the supported app’s actual view to judge the result; one preferred size need not make every screen layout identical.
Install fonts for documents
Apple’s documented workflow is to obtain an app containing fonts from the App Store and open that app to install them. Manage installed fonts under Settings > General > Fonts.
Choose the font within an authoring app that supports it. This is a document-font workflow; changing the text-size slider is a different operation.
Separate size, zoom and font family
A larger size changes the scale of letters. A different family changes their design. Before adding a new font, try the setting that addresses your actual reading or editing problem.
Check a short label and a longer paragraph. If only one app is troublesome, review that app’s text controls rather than assuming the same setting governs every view.
Choose a family with the right context
Read typeface versus font before choosing files. For design examples, compare the sans-serif collection; a browser specimen demonstrates a family’s appearance, not automatic availability in your iPhone app.
Keep the original wording and the font source with an editable document so a teammate understands what is required.
Your questions, answered.
Does making text bigger install a new font?
No. Text size and font installation are separate operations.
Where are installed document fonts managed?
Apple documents Settings > General > Fonts.
Will every app look identical after a size change?
No. Check supported text in each relevant app and its own display options.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.