iPhone app will not accept my login credentials

Thank you for trying to help me.  I really appreciate it; this is all something my husband did so easiy and so well.  I am struggling....(sigh).

What I should have said is:

I cannot log in to Dropbox on my iPhone using either the app or the Dropbox.com website using Safari.  I am logged in to Dropbox just fine on both the desktop and laptop computers.  But when I try to log in to Dropbox on the phone, using those same credentials I get the standard 'invalid email or password' message'.  (Seeing as how the logon and password work on the macbook and iMac - do you still think I should change the logon and password?)

When I look at my account information at Dropbox.com, it shows both computers as linked, but the iPhone does not appear on the list.  

And here's a little more background that may have something to do with things....

Some months ago I downloaded Dropbox app to the phone and thought everything was fine, but really did not use it.  I had a different logon and password.  Sometime later, I realized that I was not able to see or access any of the same files from the phone that were on the computers, and so I suspect I must have created an entirely different account.  In any event, today I deleted the app from the phone, powered down the phone, waited, powered the phone back up, downloaded the Dropbox app from the App Store again.  And this is when I am unable to log in using the same logon and password that works on the computers.  I am trying all this with the computers on and logged in to Dropbox.

I know I am missing a step in here somewhere.

I really appreciate anything you can do to help me.