Size of integer in PHP depends on machine, it has 32 bits on 32-bit architectures, and 64 on 64-bit architectures.
On 32-bit machines PDO for PostgreSQL always convert bigint
numbers returned by server to string. Never cast to integer even if
value of bigint would fit in 32-bit signed integer.
Type bigint is returned for example by COUNT and SUM functions.
On 64-bit machines there is no such problem because PHP integer is the
same as bigint.