It's most likely the opposite. People have no idea how to keep their desktops/laptops secure and it is much worse then it comes to the mobile area where apps can have access to almost everything. Another problems would be apps that carry hard to remove exploits (tends to happen in android). It is not possible for a smartphone to be safer than a Linux machine solely dedicated for a wallet, running behind a hardware firewall.
Using desktop has much more risks, so many virusses, links, downloads, can cause a robbery.
There are two risks to this. You can have a less technically secure desktop but it is more likely to not be stolen or you can have a smartphone which is technically more secure but more likely to get stolen, lost, or broken. With a desktop, you can control everything and all the software installed on it. You can't do that with a smartphone. A desktop can also be configured to have encrypted hard drives, sandboxing, and whatever else that makes smartphones more technically secure. After all, a smartphone is really just a tiny computer. Desktops can also download the full blockchain so you aren't relying on someone else for the right data. A proper cold storage desktop wallet cannot download viruses and should not have anything on it except for the wallet software. Also, a desktop cannot be as easily stolen, lost, or broken as a cell phone is.