Before reciting the amidah for mincha many nuschot add the sentence כִּי שֵׁם ה' אֶקְרָא, הָבוּ גדֶל לֵאלהֵינוּ before אֲדנָי שפָתַי תִּפְתָּח וּפִי יַגִּיד תְּהִלָּתֶךָ.
Why is that sentenced added specifically at mincha?
According to Halacha you are not supposed to have a break between Geula and Tefila by Shacharis and Maariv. However by Mincha there is no problem of having a break, therefore we can say this extra Posuk. You may ask then isn't אֲדנָי שפָתַי תִּפְתָּח וּפִי יַגִּיד תְּהִלָּתֶךָ a break. The Gemara in Brachos 4b asks this question and answers אלא התם כיון דתקינו רבנן למימר ה' שפתי תפתח כתפילה אריכתא דמיא that since the Chachamim instituted this Posuk therefore it is considered part of the Tefila. Perhaps by Mincha to indicate that one may break therefore we say this additional Posuk.