I *think* you did not define the stephdl repository....
Error: Package: smeserver-phpmyadmin-4.0.10.2-2.el6.sme.noarch (stephdl)
To see immediately if you have defined all required repo's you can enter:
yum install --enablerepo=stephdl --enablerepo=epel --enablerepo=smecontribs smeserver-phpmyadmin