Physical reads are not reported in pages, but in buffers, that is, the actual number of times Adaptive Server accesses the disk.
If the query uses 16K I/O (showplan reports the I/O size), a single physical read brings 8 data pages into cache.
If a query reports 100 16K physical reads, it has read 800 data pages into cache.
If the query needs to scan each of those data pages, it reports 800 logical reads.
If a query, such as a join query, must read the page multiple times because other I/O has flushed the page from the cache, each physical read is counted.