I am going to China. If I take my Samsung smart phone and get a local SIM card for calling only (no text, no data), turn off wifi, Bluetooth, and NFC, should my phone be safe as far as the stored data is concerned?
If you don't care about your calls being monitored, you could backup the stored data and reset the phone before the departure, reset it again and restore from the backup after coming back home (as R15 suggests).
However, you need to keep in mind that Chinese intelligence agencies occasionally enter hotel rooms and perform low-level copies of your laptop and phone (some kind of "forensic acquisition", like those made by conventional law enforcement agencies). Factory reset may not be enough and a skilled attacker may be able to recover the erased files. You can mitigate, but not completely remove, this risk
a) either by moving your sensitive files to a removable card (which you cannot bring to China), overwriting the memory with random notes, irrelevant pictures, and so on, encrypting the phone, and factory reset it,
b) or by simply buying a burner phone.
You should also be careful about charging your phone.
It's possible to replace your phone's charging equipment with a malicious doppelganger while you're gone, or even while you're asleep.
If you spend enough time in hotels, you may run even into hotel employees who actually enter your hotel while you're asleep. Even if you've bolted the doors and locked them.
Note that this risk could be mitigated by buying a cheap burner (dumb)phone. "Dumbphone" batteries usually last for a rather long time, which means that you may be able to stay in China for, say, a week without having to charge your phone.
It depends on your risk profile. You can assume Chinese intelligence services will be just as liberal as their western counterparts to infect hardware if not more so.
You can blindly assume cell towers are controlled or spoofed in China. If you are of special interest to state actors chances are good an exploit will reach you over those cell towers.
The only way to proplerly guard stored data is to encrypt it well. But then you still need to guard the device to protect the keys.
But hey, seeing as phones are generally manufactured in China any damage will probably already be done.