If you are a US citizen, they are not entitled to your unlocked phone. They need a judicial warrant if they want you to unlock your phone with a PIN/password. It is settled case law that that falls under your protections under the 14th Amendment.
They can take it for a "reasonable amount of time" (inconvenience you for a few hours and make you miss your connecting flight) while they copy an encrypted image. They then must return it to you.
If you are a US citizen, they are not entitled to your unlocked phone. They need a judicial warrant if they want you to unlock your phone with a PIN/password. It is settled case law that that falls under your protections under the 14th Amendment.
They can take it for a "reasonable amount of time" (inconvenience you for a few hours and make you miss your connecting flight) while they copy an encrypted image. They then must return it to you.
But did they? Was there an actual investigation going on?