Hi, my name is Kelly, and I'm an independent consultant and I'm here to help.
Yes, you can change the font size for writing emails in the Outlook app on your iPhone. Here's how:
Open the Outlook app on your iPhone.
Tap on the "New Email" button to create a new email.
Start typing your email.
Select the text you want to change the font size for by tapping and holding on it.
Tap on the "Aa" button that appears above the keyboard.
Use the slider that appears to adjust the font size to your desired size.
Continue typing your email.
By changing the font size in the email on your iPhone, it should also affect how it appears on your Mac.