Depends how you see the relevant market. You could define the market as browsers for iPhones, instead of browsers for all phones. After all, it’s not like users switch readily between different phones for different apps. There’s a whole body of case law on what the relevant market is. The gist is that it turns on substitutability, but it’s more complex and flexible. Easy knob to turn to account for tech platform dynamics.
If the friction is high enough, antitrust law has always seen that as bearing on the definition of the relevant market. You can’t lock people in and then start charging monopoly prices with impunity. One issue is what happens when the stickiness is mostly psychological friction instead of something that an economist analyzing rational action would see as a barrier. These are laws for people, after all, not for hypothetical rational beings.
