slab built bonsai pots / suraabu de tsumerareta bonsai hachi (スラーブで積まれた盆栽鉢)

"slab built bonsai pot" can be translated as "suraabu de tsumerareta bonsai hachi" (スラーブで積まれた盆栽鉢).  This phrase indicates that the bonsai pot was constructed using slabs of clay that were stacked or layered to create the pot shape, instead of being formed on a wheel or by using a mold.