"These are new phones"
Translation:Hizi ni simu mpya
Because A) simu is an N/N class noun, and their adjectives take no concords, neither in the singular nor in the plural: meza kuwba: 'a large table' / 'large tables', and B) there are exceptions to this rule, depending on the first letter of the stem of the adjective:
d, g, z : get an n-, meza nzuri: 'a nice table' / 'nice tables',
b ,v, p: get an m-, meza mbaya: 'a bad table' / 'bad tables'. (but p only when monosyllabic).
Since -pya is monosyllabic (!), it become mpya for N/N class nouns.