However, is the assumption that they can basically hack in your phones with wireless methods true ?
It depends on who you mean by “they”, but generally speaking, no, that’s not true. If you mean by the government or border agents, they won’t hack you remotely, they would just take your phone themselves. And if you mean attackers on airport public Wi-Fi, just make sure to follow @SkewedZeppelin’s recommendations below, since he basically covers all bases imo, and you should be fine.
I would recommend turning off your phone when you go through airport security though, as that will put it into BFU (Before first unlock), which means it’ll have stronger encryption, and will be harder to break into if it is lost/stolen or confiscated for whatever reason. Like @Valynor said though, this may only go so far, since they’ll probably compel you to unlock it anyways if you are “selected”. Related
Depending on your threat model, it may be worth it to not carry your main phone with you while you travel, but it depends. I’ll also add that with international travel, it’s a much higher risk that you will be “selected” or questioned than domestic travel, so you could factor that into it as well.