Magically shifting from the Ethereal Plane to the Material and vice versa is not teleporting. They are parallel dimensions. If a phase spider shifts into the Ethereal Plane, they still have to move up to you physically.
So, as a bonus, they disappear and move up to you. They could sit in the Ethereal for rounds. Then, as a bonus, BAM! They suddenly appear and attack.
THAT is a phase spider. Ninja assassins close range attackers.
And this would add so much more tactical depth to the game than Larian turning Phase Spiders into yet another enemy that jumps or teleports and has added ranged efficiency.
Larians obsession for ultra mobile combat on wide open vertical maps is killing the tactical depth of 5e. What we don't have is Ethereal predators who surprise you in melee range or more confined spaces for battlefields. But we have an endless horde of enemies who have been given teleport abilities and extra ranged and aoe surface attacks.
