1. Type some text
2. Highlight a word that you want to turn in to a hyperlink
3. Click the "Insert Link" button
4. Notice that the word you typed previously has not been copied to the "Text to display:" or "Label" field on the "Insert Link" box, meaning that you have to re-type it.
When one highlights a word, one expects any subsequent action to be applied to it. This does not happen when inserting a hyperlink in oxwall. I'm sure it's just a bug that needs fixing.
if it gets enough voices, we'll consider implementing it.
In the meantime this is considered as a custom code modification, you need to do that on your own or hire a programmer: http://www.oxwall.org/market/specialists
I will move this post to the custom code modification section, probably some community member will assist you to achieve that.