php - Desktop site's inner pages do not redirect to corresponding mobile page on phone -

i have php site automatically redirects mobile site when viewed mobile phone. have come across works home page, not rest of pages.

when access "www.abcd.com" phone redirects "m.abcd.com". when try "www.abcd.com/about-us", not redirect "m.abcd.com/about-us" "m.abcd.com" home page.

how can fix rest of desktop pages redirect corresponding pages when accessed on smartphone? htaccess fix?

there code within index page redirect m.abcd.com depending on user agent. need copy code rest of pages, or include in shared code pages.