Not recieving all emails when checking via the website but is present when I check my phone

When I log into my email via a web browser I don't get all my emails.  Then I check my email on my phone and they are there.  It just seems random what emails are not being recieved.  I have tried different browers and different computers and still the same.  I have forward the emails to myself via the phone and I recieve them.  I need to recieve all my emails when I am at a computer.  Thanks for the help.