Even if you set a passcode on your iPhone you maybe less secure than you might think. Buried under FaceID security settings you can tweak what is available on your lock screen when locked. I’ve included the above screen shot that shows how mine is locked down so that even if I lose my phone I’ve done all I can to secure it.
Head over to Settings then FaceID & Passcode. Scroll down and you will see the settings above. If you copy mine then it’ll be locked down.