HI Good day! 
how to send a file through messenger using phone? 

first that you need to do is open your GOOGLE CHROME
and second Search MESSENGER.COM 
then click then 3 dots on the right side on your google chrome 
then click the DESKTOP SITE
then LOG-IN your account 
tapos i-click mo yung  account nung pagsesendan mo ng files
at pindutin ang plus sign sa baba at pindutin ang PICTURE sign at pindutin ang FILES at puntahan ang folder kung nasaan ang iyong isesend.

sana'y maintindihan niyo.
just comment below kung may hindi kayo naintidihan