Can I replace Android with Linux on a Sonim XP10?

I wouldn't assume a Linux phone distribution will work on the XP10 just because it runs on another phone. Phones need model-specific support for the hardware, including things like the display, cellular modem and touchscreen. Even when a system boots, some features might not work.

I can't confirm a supported distribution for this model from the information here. Check each project's supported-device list for the exact XP10 model before trying any installation instructions. If it isn't listed, getting it running may require development work rather than a simple install.

Try Termux if what you want is a Linux-like command line. It runs as an app on Android, so you can learn shell commands and use packages without replacing the phone's operating system.

Android already uses the Linux kernel, though that doesn't make it the same experience as a typical desktop Linux distribution. Termux gives you a way to explore some of that environment while keeping Android.

The bootloader is another hurdle. That's the part that starts the operating system, and phones often lock it to prevent unofficial software from booting. There are reports that Sonim phones have locked bootloaders, but check the XP10 specifically before treating that as settled.

Don't flash a file intended for a different phone, even if the model names look similar. A failed attempt can leave the device unusable, and unlocking or reinstalling software may erase its data. Back up anything you need before experimenting.

If the goal is a phone that runs a conventional Linux system, you might have better luck choosing the device around the software rather than starting with the XP10. Look at the supported-device lists for mobile Linux projects and check which features work before buying anything.

Sailfish OS supports some phones, for example, but support for another model doesn't imply support for this one. It's also worth checking whether a listed device meets your needs for calls and mobile data.