Yes, he's (supposedly) a Democrat. It would probably be a little more accurate, however, to call him a Dixiecrat, as his beliefs would appear to mirror that faction much more closely:
The Dixiecrat party was a segregationist, populist, socially conservative splinter party of the Democratic Party in the mid-20th century who were determined to protect what they saw as the Southern "way of life" against what they perceived as an oppressive federal government.[1] Link
Okay, he was a Civil Rights attourney, but you really can't say he was in it for the good of his clients, regardless of how he chooses to remember it or what the man claims. He was a scuzzball who settled for pennies, and then turned around and sued his own clients to collect his fees. He was eventually disbarred for perjury in Kansas, and gave up his Federal law practice after raising false charges against Federal judges. Monumental failure^10.
Yes, he alledgedly supported Al Gore and raised money for him--though this is in doubt, as Gore does not acknowledge it, and the testimony seems to come mainly from Phelps himself and one of his sons. So take it with a grain of salt. From Wikipedia:
Phelps supported Al Gore in the 1988 Democratic Party primary election.[38] In his 1984 Senate race, Gore opposed a "gay bill of rights" and stated that homosexuality was not something that "society should affirm".[39] Phelps has stated that he supported Gore because of these earlier comments. link.
No, he's very much not a liberal or a social progressive. Any meager support he might have had for Gore based on what seems to have been one throw-away comment died early on, to the extent that the clan of harpies descended on Gore's father's funeral to protest as is their usual MO. He's a theocratic authoritarian fascist who seeks a return to Old Testament law. But as usual, Conservapedia has conflated "liberal" with "Democrat."
He's a democrat in name only, the rest of the party, every other American political party. and the entire sane human race collectively view him as a waste of space and skin, and Conservapedia is still run by yammering ultra-right nutbags who are looking for any possible way to smear anyone who is politically farther left than Ronald Reagan. Status quo.