You are right about that they will make it difficult for you to enter the country if you don't cooperate because they must make sure everything is safe both what is coming to the country and what is going out of the country but if we take look at it very well, checking on someone app is not their duty, I don't hold something valuable of BTC in your app is illegal unless the agent wants to collect a bribe with you and start doing some unnecessary searching, nothing can be hidden in the wallet if not a coin, any agent who asks for your phone and wants to check your wallet is not an agent, he is a criminal or he is a thief because I don't know what they looking for in someone private saved, but it depends on the country you are living or the kind of agents the rules guide your country.

The best way to be safe with the agent even when they enter your phone and would not find anything is to save your seed phrase somewhere else, if you have someone you trust like your dad or mom you can write it and send it to them as a message and also send your coin to someone who you trust after you have passed the agent checkpoints or getting to another country the person can send you your coin and you can also go through the message you send to who you trust and get your seed phrase to be able to have access to your wallet without any stress.