How To Sign Forms On Your Phone
(pics and example from IPhone, but may be similar on other smartphones by marking up a PDF or picture)

Step One: From your email, click on the attached PDF.

Step Two:  Press the Markup button

Step Three: Select Marker

 Step Four: Sign on line (some consents require initials in other spots)

(You can enlarge the image to sign by using two fingers)

Step Five:  Press Done

Step Six: Select Reply All

Step Seven: Press Send