Monopoly isn't defined by share of whatever market description you find convenient, it's defined by pricing power: whether the seller can raise prices over some range without losing sales to competitors. There's lots of times when things in what intuitively descriptively are the same market by some product description are different markets in practice because people don't, in practice, substitute between them in response to price movement.
A monopoly (from Greek μόνος mónos ["alone" or "single"] and πωλεῖν pōleîn ["to sell"]) exists when a specific person or enterprise is the only supplier of a particular commodity.
Apple are far from a monopoly, they don't even have a majority of the phone market, their PC share is still in single digits.