The article doesn’t list a single reason why you shouldn’t buy an IP69-rated phone.
All it says is that a higher certification level doesn’t always mean better protection from water ingress in real world conditions.
The argument that IP69 is worse than IP68 because it doesn’t include an immersion test is nonsense.
A phone that stands up to high-pressure water and steam jets from all directions won’t suddenly fail from unpressurized water.