Jumping back in on this - The XP is WAY off unless its a bug. I just killed a phase spider and got 5XP per character. Phase spider as written is 700XP. I get a bit of adjustment, but this is a hard nerf.
Large monstrosity, unaligned
Armor Class 13 (Natural Armor)
Hit Points 32 (5d10+5)
Speed 30 ft., climb 30 ft.
15 (+2) DEX
15 (+2) CON
12 (+1) INT
6 (-2) WIS
10 (+0) CHA
Skills Stealth +6
Senses Darkvision 60 Ft., passive Perception 10
Challenge 3 (700 XP)
Ethereal Jaunt. As a bonus action, the spider can magically shift from the Material Plane to the Ethereal Plane, or vice versa.
Spider Climb. The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Web Walker. The spider ignores movement restrictions caused by webbing.
Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: (1d10 + 2) piercing damage plus (4d8)poison damage. The target must make a DC 11 Constitution saving throw. On a failed save the target takes the poison damage, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.