Phones OSes are generally written so that programs cannot be installed unless they are apps, which are regulated by app stores, in part specifically to stop the spread of malware.
PCs are actually pretty locked down these days. When software is trying to install, you get a security pop up asking for permission to install. Apple goes an extra step by making you have to take multiple extra steps to install anything Apple hasn’t verified as safe. Problem is, most people just click yes without thinking anything of it, or set up their computer with permissions to install whatever, because they thinking the security pop ups are “annoying”.
You can pretty easily get malware on a phone though, especially on Android, which has a less thorough vetting process and allows you to install apps outside of the App Store. It’s just that phone malware does a better job of staying hidden, for example, by looking like a legit app but harvesting your data.
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