USB-C connector locking mechnism?
The USB-C plug has retention springs inside the shell:



(diagram excerpted from USB Type-C Cable and Connector Specification, Release 2.0).

The specified extraction force for a USB-C connector, from the same specification document, is between 8 and 20 newtons (1.8 - 4.5 lbf) when brand new and 6 and 20 newtons (1.35 - 4.5 lbf) after 10,000 insertion/removal cycles. The lower end of this is enough to "dangle" most phones (my phone masses 190g, which means it weighs about 1.9 N) as long as you don't swing or jerk it around.