Open iPhone's Photos app. Open the photo you want to add captions. Tap the Edit button. Tap the More button. Tap Markup to open your photo in the Markup editor. Tap the Text button. Tap the text box and select Edit. Type your text using your keyboard and press the Done button above your keyboard. Select a color for your text. Tap the AA button to edit your font, text size, and alignment. Click Done to save the text to your photo.