OK. I'm sorry to trouble you, but could you call her up and ask when they may have it available again? If it is possible, could you find out about it and let me know before the end of the day? Thank you in advance.
I understand. Sorry to trouble you, but is it okay if I want to ask by phone too? If it's possible, I think I can give you the result today. Thanks in advance.
"but could you please call me" の部分ですが、"but could you ask her/him by phone?"に換えます。すみません。