How to assemble code for ARM?

For x86, I used NASM - Assembler for Intel architecture , it generated an .o file, which I compiled happily using gcc.

Now, I want to write ARM code and run it, I was told to use armsim#:

ARMSim# is a desktop application running in a Windows environment. It allows users 
to simulate the execution of ARM assembly language programs on a system based on 
the ARM7TDMI processor.

But I'm just writing code (for ARMv7) and pressing a button to load & run, I don't get to assemble (.o)/compile it (.exe for windows) manually, as I did for x86.

I assume I can't do such things on x86 because it's not the same architecture, but I happen to have a ARM processor, which is on my phone ARM Cortex-A53 and runs Linux! Android.

So I would like to copy the .s file to my phone, assembly it and compile it manually. I've been googling a little, but most the stuff I find is to emulate ARM (Android Studio, Virtual Machines) and such, which I don't want...

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