Check for unusual pop-ups, redirects, or fake virus alerts in Safari
Review installed apps for anything unfamiliar
Delete any suspicious apps immediately
Check battery usage for unknown apps draining power
Check cellular data usage for unusual spikes
Restart the iPhone
Update iOS to the latest version
Clear Safari history and website data
Remove unknown calendar subscriptions
Check for unknown profiles in Settings > General > VPN & Device Management
Run a security scan using a trusted iPhone security app
Reset all settings if problems continue
Back up important data and restore the iPhone if needed