Phase Spider Stat error?

So I was looking at monsters amd I noticed two possible errors I can’t find the reason for on the Phase spider.

1) Why is his bite 2d6. The monster rules have a large creature at 1d8 and a huge at 2d6. None of the feet’s explain this boost.

2) the STR bonus to bite is a +7 when the STR mod is a +5. Where do these other 2 points come from?

Specific overrides general the general rule is large bites are 1d8 phase spider was given 2d6. As for the dmg since the bite is its only natural attack it gets 1.5xstr to damage.

The bite damage table that you are referencing is a guideline, not a requirement. Many creatures have larger or smaller damage dice on their natural attacks without explanation. For example, the Small Earth Elemental has a slam attack of 1d6. However, a Small creature's slam should be 1d3.

Its bite is its only attack, so it is getting 1.5x str modifier to damage.