How to select all text in a web page document every time?

I like to use AI to summarize tediously long websites and documents, like scientific papers or other long winded academic type articles. Yet much of the time I have to manually select all the text by holding until my phone selects a word then manually dragging the selection up and down the page. Sometimes I see a “select all” option but not always.

There has to be an easier way right? Does anyone know of any?