Hi...I’m not familiar with Frontier or their CC...sorry..maybe someone else is.....
A lot of us here start with Chase since they have a 5/24 rule meaning they will only approve you for their cards if you have opened less than 5 personal than $800 a month on a card....are you using one for your insurance phone, cable, utility bills....the cards with the highest sign up bonuses require you to spend between a $3k and 5k on the card in the first 3 months...the CSP or CSR.....
Chase also has the Freedom or freedom unlimited which have a 10,000 UR bonuses after spending $500 in the first 3 months...
You could cash out the URs to help pay for flights if you wanted to