Physical device small enough to be quickly stolen: Not Secure. (this is self-evident: physical access to device is Game Over)
Low battery requires plugging in a cable to charge; the cable may be a surreptitiously-installed data cable. I do not trust the hardware or software stack that handles the data cable to be secure.
SMS: Not Secure. http://www.cybersecuritytrend.com/topics/cyber-security/arti...
Wifi: Not Secure. https://www.bestvpn.com/privacy-news/wpa2-wifi-not-secure/
Many apps "require" silly amounts of permissions to the phone before they'll install. Apps' ability to read what's on screen, to be notified of clipboard changes, to listen to sounds; all when not even in the foreground. On my computer, I can easily check what apps and background services are running. Not so easily on a phone.