Why is earth pin absent in phone chargers plugs but present in laptop ac plugs?
In the EU (and probably in many/most other regions too) appliances that are double insulated, or which work from safe extra low voltages (SELV) are not required to be connected to protective earth.

In your first example, if the "wall-wart" is properly constructed, a single fault would not result in dangerous voltages being present on the low-voltage† lead from the wall-wart to the phone (and thence to you) 

See also


Why is it safe to touch the chassis of a tube amplifier and something earth grounded simoultaneously?
Grounded Common AC-DC Power Supply Simple Circuit


† Typically 5V nowadays and maybe 1000 mA or so for a phone charger.