Apparently the Tibetan word for “lap” or “bosom” would be pang pa (as in pang du len “to take [e.g. a child] in one’s lap”). But in some languages/dialects, it would be phang ma (as in rDzong-kha: phang mar btab “to embrace/hug”). Also Jäschke gives phang as a variant of pang?
And I have a feeling that phang in the sense of “lap/bosom” is somehow connected with the verb phang ba (“to be affectionate” or “to cherish” or “hold dear” as in gces shing phang/s. But Jäschke seems to record only phang ba in the sense of “to be use, spare, to use economy,” “to be thrifty/frugal.” This latter meaning, I think, is secondary.