Plugging a mic into a phono input, Do I need to use a transformer?

I bought an unknown tube pre amp and the seller said that most likely radio/turntable console. It has mono rca connector in and out which are just marked analog. I plugged an SM58 into it with an XLT to RCA cable and ran the out to my studio mixer to see how it sounded. To my surprise it sounded great. Clean, warm and plenty of gain. I'm going to mount panel mount XLR and 1/4" ins and outs. My question is if it is RIAA phono how does that impedance compare to a standard 600 ohm mic pre? Should I mount a mic to line or mic to something transformer to get the most out this thing? I'm not worried about the output as I can use simple direct box components to get the correct levels for going into compressors and recording inputs.

First of all, you will have to disable the RIAA correction in the phono channel.
This filter network boosts the lower frequencies and attenuates the higher frequencies.
(This probably explains the 'warm' sound...)
Usually this is a matter of removing two capacitors.
As far as I know, the input impedance of a (moving magnet) phono input is in the order of 47 K.ohms.
A matching transformer (something in the order of 1:6 or 1:7) will improve the S/N ratio and increase sensitivity.