You'll see, as is discussed in the many other threads on setting up anchors, that you do indeed need to specify the complete URL.
So, if this is something that you expect to do often and the actual anchor point is in the same spot on every page (ie: top of description is the most common place people think they need to put it) and your clickable link to take you back to that anchor is also always in the same spot (ie: bottom of description, usually for the same reason), then you can easily put that into your TEMPLATE instead of trying to be inserting custom HTML and PHP into your product descriptions needlessly.
It would really help if you were to explain the business reason behind why you're even trying to do all this, instead of just bashing at a pre-determined end solution that's not working for you.