I can’t get the nsec.app to work on my phone. Can you recommend a browser extension? Thanks! 

 nos2x for Chrome, Alby, and Flamingo are what I am aware of.

https://chrome.google.com/webstore/detail/nos2x/kpgefcfmnafjgpblomihpgmejjdanjjp

https://getalby.com/

https://www.getflamingo.org/ 

 Which phone and browser?