serialportlist('available') can tell you whether the port of interest is "available"
serialport() objects appear to try to open the port as soon as you invoke serialport() . They do not have a connection status because serialport() fails if it is not able to open the port. The port stays open until you clear the serialport() object.
This is different than the older serial() objects, which had a specific fopen() and the properties could be examined to see if the serial() object was open.