Yeah - that’d be a sockpuppet account. Not a “burner” account.
Burner or throwaway accounts are short term one off accounts used for a specific topic/question and meant to be tossed.
Sockpuppet accounts are long time accounts used to buttress a known account or to discuss topics that some would like to punish.
Getting a genuinely anonymous phone or account seems challenging these days.
This account seems more like an Alt.
You mean like Pierre Delecto, Mittens Romney’s secret Twitter account.