How to change the from email address on my iPhone?

I have a gmail account for work but email from that account using my @companyname.com email address.
How can I send emails using @companyname.com from my iPhone rather than @gmail.com?

Click on the current From address and then you will have the ability to change to other accounts (only if you have added them).

There's a way to set the Default Email Account in Settings > Mail.

Hope that helps.

Yea it is in the settings like the previous person mentioned. If you need help you can contact easysmartphonesupport.com. They are pretty and cheap.