Check your settings on each. You want to leave messages on server after downloading them. You may also find it easier to use IMAP instead of POP to access your email from both places. I use POP with my xfinity email but still can get all email at my pc or my phone with no issues.
This is where you need to be in gmail on pc.
Go to settings and then to "forwarding and POP\IMAP" settings.
What is currently enabled there? pop or imap?
Also go to your email server settings on your phone and see how it is setup there. They must match, meaning both must be pop or both must be imap.