> Ablation (Latin: ablatio – removal) is the removal or destruction of something from an object by vaporization, chipping, erosive processes, or by other means. Examples of ablative materials[clarification needed] are described below, including spacecraft material for ascent and atmospheric reentry, ice and snow in glaciology, biological tissues in medicine and passive fire protection materials.

https://en.wikipedia.org/wiki/Ablation

The poster is saying that a case can wear out and be replaced without damage to the phone. You can let the case take all the damage, then get a new one. But if you let a phone take all the damage (even if it's a tougher phone), you can't remove that damage.

I think they meant in the sense of it being worn away and destroyed as an intended use.

Adjective definition 3 from https://en.wiktionary.org/wiki/ablative