Basically, UART serial console is available on most Nexus phones and tablets. To access UART interface on Nexus you would need to connect to the 3.5 mm audio using custom built debug cable and also specific version of serial-to-USB adapter that works with 1.8 V voltage levels (not 3.3 V like those made for Arduino, Raspberry Pi, etc).

Here are some links for your reference:

• http://www.abclinuxu.cz/blog/Lorris/2013/12/serial-console-on-google-nexus-5
• http://www.pabr.org/consolejack/consolejack.en.html
• https://www.reddit.com/r/Nexus5/comments/23lilk/buildinganexus5uartdebug_cable/