For a mid-range Snapdragon phone with 6GB RAM, I’d recommend starting with Vulkan, 1x native resolution, and default speed-hack settings when using aethersx2 for ps2 on android. Switch to OpenGL if you experience graphical glitches, and avoid aggressive hacks because they can cause compatibility issues.
Use a legitimate PS2 BIOS dumped from your own console. For an alternative, consider NetherSX2, a community patch project based on AetherSX2.
Keep in mind that performance varies by game, and audio crackling usually indicates that emulation is struggling to maintain full speed.