The essence of prayer in a minyan is praying Shemoneh Esrei together with ten Jews. One who does not succeed in praying Shemoneh Esrei together with the congregation should pray with the chazan when he repeats the Amidah (Chazarat HaShatz) since, according to most poskim, that is also regarded as prayer recited in a minyan.
Additionally, if a person arrives late to synagogue and recites the Amidah while the congregation is still reciting other parts of the prayer service, such as Aleinu Leshabe’ach, although he is not considered praying in a minyan, he does derive some merit, since he is praying in a holy place where ten Jews are singing songs of praise. If he recites the Amidah of Shacharit while the congregation is praying Musaf, he is considered to be praying in a minyan (Tzelach, Berachot 6a; Mishnah Berurah 90:30).
A person who is unable to attend synagogue should try to coordinate the time he prays with the time the congregation prays, thereby partially engaging himself in the minyan’s prayer. This way, his prayer will be accepted, since the time the congregation prays is a favorable time (Berachot 8a; ShulchanAruch 90:9). Lechatchilah, he should try to synchronize his prayer with the prayers of a specific congregation whose schedule he knows. If he does not know when a particular congregation is praying, he should have in mind to pray with any minyan, for surely any time he prays there is a minyan somewhere in the world that is standing in prayer.
. Eshel Avraham Butshatsh 52 maintains that prayer with the chazan as he repeats Shemoneh Esrei is considered prayer in a minyan and that is also the opinion of the Chatam Sofer. So write Kaf HaChaim 90:63 and Yabia Omer, part 2, 7, as well as the majority of poskim. By contrast, the Pri Megadim (Eshel Avraham 52:1 and 109:4) writes that the essence of prayer in a minyan is that ten Jews pray the silent Shemoneh Esrei together (this can be inferred from the Rama 109:2 as well). So writes the Igrot Moshe Orach Chaim, part 3, 9, and is implied from the Mishnah Berurah 90:28 and 52:6, as well. However, Beit Baruch 19:35 attests to the fact that the Chafetz Chaim himself would pray with the chazan so that the chazan would not wait for him to finish his prayer. In conclusion, it is best to try to pray silently with the congregation in order to fulfill one’s obligation according to all opinions, but even praying with the chazan is considered prayer in a minyan according to the majority of poskim.
Further, it is implied from the Mishnah Berurah 66:35 that the essence of prayer in a minyan is that one begins to recite the Amidah together with the congregation. However, most poskim write that even if a person is a few berachot ahead or behind, he is still considered to be praying in a minyan, as written in Yabia Omer, part 2, 7, based on the Pri Chadash and others. The Acharonim also disagree concerning whether or not the prayer of six people praying together with four who already prayed is considered prayer in a minyan. Yechaveh Da’at 5:7 considers it to be prayer in a minyan, whereas, Igrot Moshe, Orach Chaim, part 1, 28, writes that it is not considered prayer in a minyan, yet they are permitted to recite matters of sanctity. In conclusion, there are different levels regarding the status of prayer in a minyan.
. Halichot Shlomo 5:18 writes that the virtue of coordinating his prayer to the time when the congregation is praying applies specifically when the individual praying intends to join a particular congregation. Therefore Rabbi Yitzchak suggested to Rav Nachman that he be notified when exactly the congregation was to begin Shemoneh Esrei, so that he could have in mind to coordinate his prayer with theirs (Berachot 8a). However, the Mishnah Berurah 89:33 writes in the name of the Chayei Adam that a person praying individually may pray immediately when the day begins, for surely in big communities there are minyanim at that time and if so, he will certainly be praying when a congregation is praying. It seems that when a person cannot be physically present with the congregation, there are different levels. The highest level is when an individual has in mind to coordinate his prayers with the prayers of the minyan in which he prays daily. The level below that is when a person coordinates his prayer with a different congregation in the area where he lives. An even lower level is when he synchronizes his prayer with a congregation praying in a different place. The lowest level is when he has in mind to coordinate his prayer with any minyan that is praying at that moment, for probably anytime he prays, there is a minyan praying then. See Avodah Zarah 4b and Rabbeinu Tam’s explanation in the Tosafot.