This is technically true, but there are two additional scenarios that should be considered:

(1) The police could lie in their written reports and say that you voluntarily consented to the unlocking of your phone. If so, then it becomes an issue of your word against theirs when testifying in court at a hearing to suppress the evidence. This is generally not a position you want to be in as a defendant.

(2) If the police want to be a little more clever and are more risk averse of being exposed as liars in their reports, they could entirely omit from their written reports any mention of the forceful unlocking of your phone, and they could opt not to use the evidence they find on your phone against you. However, by browsing messages/documents on your phone, they may discover leads that they could follow up on in order to obtain evidence against you in a way that seems entirely independent of the illegal search.

For example, they might see that you were texting "My Drug Supplier" and gather information about who your drug supplier is, where he operates, when he makes deliveries, etc. The police aren't going to write any of this in their reports, but they'll send some officers to monitor this guy. Sooner or later, your supplier will fuck up and the police will "just so happen" to be in the area when he does. They'll come up with a reason to stop him (ran a stop sign, turned without signalling, expired registration sticker, whatever), and they'll "coincidentally" find evidence to support his arrest and to obtain a search warrant. In the course of executing their now lawful search (including his own phone and related records), they'll "just so happen" to come across your name in the process and "discover" evidence that incriminates you.

The takeaway: Whether on the streets or in the courtroom, don't count on the law to protect you. The police know how to game the system better than you do, and the judges aren't exactly going to bend over backward to help you out unless the police misconduct is so obviously irrefutable that it cannot be denied. But if it's just your word vs. theirs, you are fighting a losing battle. If you can prevent the police from unlocking your phone, you absolutely should do so--regardless of the rules of evidence.