Or you could just get someone else to do it for you!! LOL!
Seriously, the jumping on Phantom's back is a really good move and very effective too, esp. in DT mode but often when he throws Dante off, he manages to inflict him with some heavy damage (well it happened to me a lot!!) so I found it useful for Dante to run around as far away as possible from him, thus increasing his health until there was sufficient for another go!
Another technique I found useful though it takes some quick reflexes, was to stand underneath Phantom when he jumps up (so he can pounce) - lam into him with 'The Guys'! You can get quite a few shots off before he makes his rapid descent - this is where you need to be quick to get out of his way coz squashed Dante isn't too nice!
Hope that helps!