Bluetooth ranges from 5-10m indoors depending on wall composition, other Bluetooth activity in the area, and the position of the connected device on the desk with the user walking away from it.
In an open-air scenario, the range can increase to 20m in perfect conditions. Weather and other RF activity will impact this.
Bluetooth is reflective, so its range will be better in the areas with more reflective surfaces (walls and glass) but can decrease for example in the park, where it can't reflect from anything.
On the human body, the range of Bluetooth to the bud can be as low as 2m (open air through the body) and pocket position can be a factor, indoors or built-up areas are generally much better due to reflections and multi-path effects.
Since the human body has blocking capabilities, actions like covering your phone, backward or upside-down position of the phone, placing it in the right pocket can sometimes influence Bluetooth connectivity or even cause a disconnect.
Please always test Bluetooth in an open-air environment.