Price Increase In A Matter of Seconds?
 

Selected a flight PHX > BOI. It showed $83. Selected it and it said it changed to $153. Went ahead and selected it. Entered my credit card info and everything, went to purchase, got an error code and had to reload, said flight then increased from $153 to $203.

What's the deal with that?

Perhaps the revenue management software was in the process of repricing your selected flight right when you were trying to buy?

Based on the early morning timestamp on your post, it is likely that a new fare file was being processed (they often happen in the wee hours of the morning when there is less Customer impact). However, it is also possible, that someone snagged the inventory for the lower priced seat out from under you. If there was only 1 seat left at that fare, and someone else clicked purchase before you could, it would move you to the next lowest price available.

Southwest's sales and inventory systems aren't synced in real time. This is unfortunately a common issue.

So I checked again and the flight dropped back to $153. What a hassle lol.

$83 fares have a 14-day advance purchase requirement. So if you were searching for flights on June 11th, the fare would no longer be available once it crossed over from Thursday into Friday last night as it would be less than 14 days away.

I've seen this type of thing happen when making award bookings. The search results page will say one thing, then when I click to book, the points required goes up by 5-10% or so. Pretty rare, but it happens from time to time.

Ah, this probably explains it.