There are a few reasons that slides may not respond.
Presentation window is not focused
The presentation window must be the top and focused window for PhonePresenter to work properly. Click on the presentation window to focus it.
Bad Wi-Fi Connection
PhonePresenter may not work well on slow or weak Wi-Fi connections. Move closer to or reorient the Wi-Fi router to get a better signal.
Blocked by a Firewall
Check that a firewall is not blocking the PhonePresenter server.
Xdotool not installed
PhonePresenter depends on xdotool when running on Linux. Check that xdotool is installed.
Conflicting with Synergy
PhonePresenter may conflict with Synergy. Temporarily turn off Synergy to fix the problem.