Looking for quality sound from my iPhone/cloud stored media

Hi all,

I'm not educated on sound equipment so hoping some of you experienced people will guide me.

I live in a small apartment and have my eye on a Polk S35 center speaker  to replace my little JBL Bluetooth speaker. 

Polk S35 -  https://smile.amazon.com/dp/B01MTCQ0UT/?coliid=IF9N95M66W6R0&colid=31ANHLF72W1EQ&psc=1&ref_=lv_ov_lig_dp_it

What I want to do is hook my iPhone to this center speaker and get a good boost in sound improvement.

After researching, I have the following questions:

1. Is it crazy to use a center speaker as a single speaker?
2. Could I hook my iPhone to the Polk via a good quality 3.5mm/2RCA adapter and get good overall sound improvement?
3. Do I need a DAC in between the iPhone and the Polk to really get my money's worth out of the Polk?

Thanks in advance to all that respond. Really appreciate your time,

Melissa