They will detain you. I know the US procedure because i was instructed as i worked there as a representative for an overseas company in Europe.
If you’re a national of the US they will detain you and hold you in detention to ask you questions. During this time your phone will either be cloned or confiscated to be decrypted at a later date. You will be released after a few hours. They will likely not bruteforce it, but rather attempt to use security flaws present in your device/firmware. They will do the same to your laptop.
If you’re not a national of the US, you will be denied entry and flown back to where you came from. This is common practice in a lot of western countries.
What you should do is not carry sensitive information across borders, by using a cloud service to sync at your destination or use hidden encrypted containers in your device. Unless you’re involved in terrorism, white collar crime, CSAM or drugs, they will never have people smart enough to find out hidden containers on you.
You’re free to do that, but seems like a good way to be put on a list to be harassed more in the future. You make a cop/border agent feel stupid and he/she will make sure to make your life harder.
The records will show you’re trying different ports of entry and if a border guard doesn’t like you, you will be selected for investigation and getting off that list may take years. Worse, you can be banned from entry for no reason and good luck appealing that.
Personally i like to treat the customs agents real nice. I call them sir or ma’am, i follow their instructions and i show them a squeaky clean phone and they let me off with a smile at the first port of entry. Being combative with an agent will not change the laws. Moreover if you have obligations to a company, they will not look kindly to this sort of attrition causing delays and will pass you over next time they need someone. This of course means you won’t get paid as much (or, depending on circumstances, at all).
I agree with the other poster, picking battles is the way to go.