Don't trust YouTube videos. Most of them will show only specific gameplay segments of specific lightweight games where they run near or at full speed, won't show the settings they used (most use settings that sacrifices accuracy and might introduce game-breaking bugs) and mostly important, they won't show the game running for long enough so you won't see the big performance hit Dolphin takes once the device's thermal management kicks in.
If you still want to buy a phone to use with Dolphin, you should aim at models with the latest flagships SoCs from Qualcomm (Snapdragon 820/835/845, etc) as they'll be the ones with the least GPU driver bugs (that doesn't mean they're perfect!). But keep in mind that no matter what you see on YouTube, most (to not say all) games still won't run with good performance, especially after the thermal management kicks in.
TL;DR currently there's no phone with enough performance or with mature enough GPU drivers to run Dolphin at decent performance...
If you still want to buy a phone to use with Dolphin, you should aim at models with the latest flagships SoCs from Qualcomm (Snapdragon 820/835/845, etc) as they'll be the ones with the least GPU driver bugs (that doesn't mean they're perfect!). But keep in mind that no matter what you see on YouTube, most (to not say all) games still won't run with good performance, especially after the thermal management kicks in.
TL;DR currently there's no phone with enough performance or with mature enough GPU drivers to run Dolphin at decent performance...
Avell A70 MOB: Core i7-11800H, GeForce RTX 3060, 16 GB DDR4-3200, Windows 11 (Insider Preview)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)