For ZigBee, what is the standard that specifies such things as Symbol clock error, EVM Offset All, Phase error, LO leakage?
ZigBee has limited specs compared to other wireless standards. The specs you need to meet are defined in 802.15.4g-2012. Section 18 is the PHY specification and section 18.3.4 is for O-QPSK PHY RF requirements.
You also need to meet local regulatory emissions. However, ZigBee is not closely specified and has very limited interoperability compared to other wireless technologies like Wi-Fi, Bluetooth, or cellular.