why has healthy green leaves fell off my orchid

[orchiddream]

, can you please help, I have approx. 20 phals in my porch and within a week the leaves have started falling off, even healthy green ones, there roots are healthy and there is no black so cant be crown rot. I think its the cold but not sure. here in the uk its cold at the minute and my porch has no heating, will it be the temperature? I have moved them upstairs in my hall now hoping for a miracle. some other leaves are limp and red too, please help.