Because the poster was talking about, using the siddur app on the phone.
One poster made such a comment, but that’s not the pint. A jammer may or may not prevent a siddur app from working, but will definitely prevent phone calls from being made.
And as far as the phone being ossur in case of emergency, that is dependent on whether Shabbos is hutrah or hudcha.
Huh? It depends whether there’s situation of pikuach nefesh. Either way, the jammers aren’t there because of Shabbos.
According to you, a person should not turn off his phone when going to shul to daven and should actually constantly look and check their phone, incase there may be an emergency.
No, according to him, the phone should be usable in an emergency.