I’ve not heard of any “tool or subscription service that” automates shill bidding, which if it were successful would be very popular with sellers.
Your best bet is to contact eBay with your suspensions.
It’s doubtful there’s anything going on, but sometimes (rare) there’s a grassy knoll.
If the seller has a high number of feedbacks, especially from buyers with larger number of feedbacks, then it’s even more unlikely something foul is afoot, because with that many auctions some other sleuth would have ferreted them out. You might also want to check out other sellers to see if this type of item appeals to bidders with low feedback.
If you’re not satisfied with eBay’s response, then simply find another seller, or find another source for these phones.