Is it enough to rise when a parent enters the building or must you rise every time he/she enters your room or passes by your room.
I am interested to know customs for both sefardim and Ashkenazim as I recall seeing a distinction.
Aruch hasulchan yora daiya 240.24 (maybe only for ashkenazim)
is not sure if you need to get up every time (as can be understood from the yerushalmi, and tosfos) or just 2 times (maybe only when in private) (once in the morning and once in the evening) is enough (as by a teacher so as to not respect him more then he respects heaven)(as can be understood from the gemoro) , he brings sources for both ways.
From the aruch hasulchan and the shulchan aruch below it can be deduced (if I understood correctly) that anyway sefardim need to get up before their father many times (as many times as they meet)
Maybe you are referring to shulchan aruch yora daiya 242.16 (end) where by a teacher there might be a difference between sefardim and ashkenazim, that sefardim need to get up every time and ashkenazim when in private (others do not see) need to get up only 2 times a day.