Thanks for the chapter!
MC seems to be gathering quite the following. I wonder how many summons can he do in a short time, and is there a constant drain on his magic keeping them there or is it just a one time big cost just to summon them? Milla mentioned that he can summon from anywhere but the magic cost increases with distance right? If they make a room next to the one he's in for all the potential summons to stay in that's not directly connected to the dungeon the hero party traverses it would save him a lot of magic to summon them while preventing the hero party from bumping into them accidently before being summoned.
In any case, Phoenix's new party member seems to be a young girl dressed like a white magic user or elemental spell caster. My bet is a spell caster of an element as the idiot jerk would protest against a white magic user who specializes in buffs but has little combat potential along with MC's comment a few chapters back about white magic users considered only slightly less useless than Black Magic users. As for element would be something other than fire as Phoenix has the sword of the ultimate fire spirit so another fire user would look bad and pale in comparison to him. Could go for an opposite element like water or ice to contrast with his fire, or something complimentary that could combine for a stronger attack like wind. Guess we'll find out next chapter.
As for the fifth level it looks like one enormous honey trap if the first room is to judge anything by. Considering the meganeko and dark haired maids have horns, and all of them have hearts in their eyes and around them I'd say they're succubi using charm. Granted succubi aren't known for being strong physically, but they do tend to be strong in terms of attack and seduction magic. After all, if go into a room full of beautiful maids like a maid cafe where they don't show any hostility and are welcoming you chances are you're likely to drop your guard a bit. Also, pure physical fighters like the archer and the idiot are usually weak to mental manipulation and Phoenix might be the only one with some resistance due to being a hero. The paladin has a tank build and the newbie can only cast magic specializing on her element so it's highly unlikely anyone can buff magic resistance or dispel a successful charm. Then the maids are likely to have practiced combining their charm magic together for an even stronger effect using their numbers. Even if can't combine their magic just being hit multiple times at once by the same spell increases the chances of the first few spells weakening resistance allowing the later spells a better chance of taking hold. Although this is just my conjecture. Could be the maids have horns because some of them are demons and are ninja assassins with weapons under their clothes rather than succubi.