I'm not sure that Pomu wouldn't fit into Phase Connect. Fishman has spent a lot of effort in getting people with idol skills and interested in idol culture in the company. Shiina, Airi, Rie and Clara have worked on being idols at some point in their lives, and Shiina, Airi and Rie have at least put in some time in an Idol school, and have interests in idol culture. There are talents like Jelly and Rie that can help with producing covers and original songs, doing backing music and so forth. Phase has a pretty strong talent lineup for singing if she wants to do group stuff. Phase has done small-scale concerts before and has a strong con presence if she wants that. Oh, and if the Lia and Pomu stream is anything to go by, I think she would find friends in Phase quite easily.
The only real point of concern I'd have is that if Pomu joined Phase, she would likely be the most popular talent in the corp, and not by a small margin. I'm not sure how that would play out in terms of group dynamics and how Pomu would feel about that.
I think Hololive and Vshojo are better options, but Phase Connect wouldn't be a bad fit.