If I am using apps on my smartphone can the network admin. see the apps I am using on my smartphone?
Some apps will use insecure communication (HTTP) and then your data will be visible. If you have a Mobile Device Management solution such as Intune, it will also report the apps you have installed and might install an SSL certificate to strip your traffic.
Also, the destination of the traffic can disclose information on the apps being used. If you want to stay hidden from a network admin, you can best use a VPN tunnel or Tor (But TOR will be a big red flag in a decent company). VPN and Tor communication can be blocked in companies.