Togetic and Togekiss both have angel-esque wings, along with having Serene Grace for an ability. Togekiss's PokéDex entry states that it brings blessings to people. No so much a "guardian angel" as a regular angel.
Gardevoir is extremely protective of its master and has flowing robes, which angels are often depicted as wearing.
Hear me out on this one. Absol appears where there is an impending disaster as a warning. However, people misinterpreted its purpose and believed that Absol was the bringer of disaster. Mega Absol's large wings and pure white fur give off an angelic appearance.
Cresselia could also be partially based off of a guardian angel due to how she wards off nightmares.
One could also say that the Tapus are conceptually guardian angels — they're elevated beings (not Legendary, but not regular Pokémon either) and they protect their islands and their inhabitants.
I think that is all Pokémon that may take inspiration from guardian angels, but if I missed any let me know!