does this happen always or straight after reboot for only one time?
after reboot when you open dialer, com.sec.phone starts running and after that it opens real fast.if you also have a long time to use dialer and your ram is loaded enough it can delay only for once again and after that everything is fast again.
could it be a task killer you re using,closing the service?do you use greenify and you greenified com.sec.phone service?do you often clear RΑΜ manually?