When troubleshooting phones, it is helpful to be able to see more detailed logging. Turning verbose logging on will show when a phone requests a file, allowing you to know the phone at least has working networking by that point.

• Edit the tftp configuration file

vi /etc/xinetd.d/tftp

• Add the "–verbose" startup option

...
        ## Customization: add the "--verbose" command-line option to see when TFTP files are requested by clients to aid in troubleshooting
        #server_args             = -s /tftpboot
        server_args             = -s /tftpboot --verbose
...

• Restart xinitd

service xinetd restart

You can grep for tftp in /var/log/messages, and see live tftp traffic with:

tail -f /var/log/messages | grep tftp