The main difference with Microsoft is that Apple does not have a monopoly in phones like Microsoft had with PCs. Apple phones make up only 13% of the phone market.
> Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors. That is how that term is used here: a "monopolist" is a firm with significant and durable market power.
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> Apple phones make up only 13% of the phone market.
iOS has 60% of the market in the US[2].
[1] https://www.ftc.gov/tips-advice/competition-guidance/guide-a...
Also it's market-specific. As the other commenter noted, the market share is region-specific and in the EU higher than 13%. In the U.S. it's even higher at ~47% (https://www.statista.com/statistics/236550/percentage-of-us-...).
You could argue that users technically have a choice to switch to Android but due to network effect (e.g. your family/friends all use iOS) and lock-in features like iMessage and Facetime, it's often a false choice.
> Captive markets are markets where the potential consumers face a severely limited number of competitive suppliers; their only choices are to purchase what is available or to make no purchase at all