Many instances of remote attacks, for example the Pegasus spyware targeting journalists using iPhones a while back. 

Snowden did an interview demonstrating why he removes hardware from his phones and only uses wired headphones. If it has a wireless radio, it can be compromised. 

Not to mention supply chain attacks where your smartphone could be compromised before purchase. This is why the community recommends open source hardware/software in an airgapped device as the only secure option long term.