Could be any number of things, but I doubt it has anything to do with the phantom power (same result with the dynamic mic pretty much tabled that thought). Phantom power is strong enough to fry delicate ribbon mics, but usually won't hurt anything else if applied accidentally.
I think there was a similar issue recently. Other than "user error" I don't recall the specifics, but IIRC it had something to do with the track Select Button and the Input/Track assignment. You may want to try a search on "playback". (Click the Site Results tab to see the hits.)
Do the 5 tracks already recorded playback ok? (I think you said they do.) If so, that eliminates any general record/playback system concerns and points strongly to user error.
Are you seeing the recorded new signal on the the Track Meter while recording and on the Track Meter and Stereo Bus Master Meter on playback? (The Track playback signal is routed directly to the Stereo Bus and the Monitor Bus. The Track Meter shows the incoming signal, and on playback shows the recorded signal level. The Stereo Bus Master Meter shows the actual playback level set by the Track Fader and the Stereo Bus Master Fader.)
If the other tracks are playing back ok, and you recorded the new Track's signal, the new signal should play back at the same level as it was recorded as long as the Stereo Master Bus Fader and the Track Fader are set to unity gain. Your post seems to say this isn't happening for the newly recorded Track.
So.....are you seeing the signal on the Track Meter while laying down the Track, but not on the Track Meter on playback? (i.e., you assigned the Input to the Track and you armed the Track, but forget to press the Record Button?) Your solution very likely will revolve around assigning the correct Input to the correct Track and arming the correct Track and then actually pressing the Record Button.
(BTW, I strongly suggest viewing, if you haven't already, all of Phil Tipping's free video series found in the Sticky section at the top of the DP-24/32 forum.)