Is phone.com.pl a good TLD? Can I quickly sell this domain, and is the TLD reputable?

This is not the way to go. It's time to stop investing in dropped domain names, as they are difficult to resell and establish as a reputable brand with their extensions.
 Instead, it's more beneficial to purchase an exact high search volume keyword .com domain. This will ensure that there is a significant monthly search volume for those keywords and also add legitimacy to your brand.