How to change wording "Show order summary" on checkout for cell phone

We noticed that the coupon code field is not visible on a checkout when using a cell phone. One has to click “Show order summary” to see it. I think a good solution would be to change “Show order summary” to say “Show Coupon Field & order summary”.

I found in languages “order summary” made the change and saved it. My changes stayed but did not change in the checkout.

Where can I change this wording?