http://revach.net/article.php?id=1708

Section: Halacha   Category: Tshuvos
Tzitz Eliezer/Pri Megadim/Chazon Ish - VaYechulu With The Tzibur In Middle Of Shemoneh Esrei
If someone is still in middle of Shmoneh Esrei when the Tzibur is saying VaYechulu, if he is up to the VaYechulu in his own Shmoneh Esrei should he say VaYechulu out loud with the Tzibur? The Tzitz Eliezer (14:24) paskens that in order to be Yotzei the important Inyan of saying VaYechulu together with a Minyan one should say VaYechulu out loud with the Tzibur. A person who has just reached the end of the Brachah of Mechaye Meisim at the time that the Tzibur is up to Kedusha should say Kedusha out loud with the Tzibur, so certainly in this case VaYechulu should be recited out loud with the Tzibur since he is not adding anything new to the Tefilah.

The Pri Megadim says that VaYechulu should be said out loud together with ten people because VaYechulu is testimony that Hashem Yisborach created the world and reciting it is a fulfillment of v'Nikdashti b'Toch Bnei Yisrael'. The Pri Megadim concludes that one should hurry up his Shmoneh Esrei in order to be able to say VaYechulu together with a Minyan.

The Chazon Ish however argues with the Pri Megadim and he says that since Davening a long Shmoneh Esrei is praiseworthy one should not hurry up his Shmoneh Esrei for the purpose of the recital of VaYechulu with a Minyan. However, the Chazon Ish would agree to say VaYechulu out loud during one's Shmoneh Esrei since he is not hurrying up his Shmoneh Esrei at all, he is simply saying it out loud with the Tzibur.  

Disclaimer: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.