The only reason I can think of for "swapping out" the Twitter phone is to check it for compromises (hacks), and improve hardening (e.g., change passwords, upgrade software). They probably do the same with the other phone.
The Politico article said that Trump uses two phones, one exclusively for calls, and one exclusively for Twitter and news feeds.
The article also said that Trump does swap out his voice call phone monthly, but may go 3+ months on the Twitter phone.
Of the two, I would assume the voice call phone is more critical to keep secure, and that is rotated monthly.