I just tested the following in Android, and I reckon it’s the same in iOS, when editing I selected the text, triggered the insert markdown link using mobile toolbar, and then paste also using mobile toolbar.
To set this up if you don’t have it setup goto settings > mobile , locate the “insert markdown link” and hit the plus icon if its not already included, and then find “paste” and do the same. Then I dragged the paste command to be next to the internal link icon.
And then it’s as easy as write the word, select it, and hit the two icons… Hope this helps and works in your version also.
If you’ve got a keyboard, you could add a hotkey for the “insert markdown link”, and then do the key combos for inserting the link, and pasting from from the clipboard.
A final option could be to have a template which checks if there are any selected text, and if not ask for the text to use, before inserting the full link with the chosen text. This template could then be hooked to either a hotkey or the toolbar.